This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This project is a comparative study of normal and pathological brain aging in humans, chimpanzees, and other nonhuman primates, with the specific goal of understanding why humans are the only primates that develop Alzheimer's disease. We are using comparative neuroimaging to identify species differences and similarities in brain gray matter volume, white matter volume, and white matter integrity across age groups. In addition, we are comparing age-related changes in microscopic brain anatomy and molecular biology in postmorten tissue. This includes documenting the varieties of beta-amyloid oligomes in humans and nonhuman primates, including forms specific to humans, and identifying ligands that bind human-specific forms.